1. Field of the Invention
This invention relates to a solid-state image-sensor camera system, for example, of a single-lens reflex type, capable of recording information by means of a solid-state image sensor and capable of permitting interchanging of lenses, to a detachably-mountable lens barrel adapted for use in the camera system, and to an accessory adapted to be inserted in between the lens barrel and a camera body.
2. Description of Related Art
In cameras of the so-called single-lens reflex type (hereinafter referred to as single-lens reflex cameras), which are arranged to have one and the same photo-taking lens used in common by a viewfinder optical system for observing an object to be photographed and by an image forming system for photographing the object, there have been proposed various cameras of such a type that a solid-state image sensor is used as an image recording part in place of the conventional silver-halide film. Hereinafter, the single-lens reflex camera of the kind using a solid-state image sensor will be called a solid-state image-sensor camera.
If the interchangeable lenses and accessories such as external flash devices, etc., which have been adapted for the conventional single-lens reflex cameras using silver-halide film are not usable for the solid-state image-sensor cameras, it is a great disadvantage not only for single-lens reflex camera users but also for camera providers.
In view of this problem, efforts have been made to provide solid-state image-sensor cameras which retain interchangeability with the system of the conventional single-lens reflex cameras. For this purpose, it has been considered to be most rational to arrange a solid-state image-sensor camera to have a solid-state image sensor disposed in a focusing image forming part equivalent to a silver-halide film on the basis of the arrangement of the conventional single-lens reflex camera using the silver-halide film. On this viewpoint, various solid-state image-sensor cameras have been developed.
In such a solid-state image-sensor camera using a solid-state image sensor, a CCD or the like is employed as the image sensor in general. In that case, an optical filter is generally attached for correcting spectral sensitivity characteristics, because the characteristics of the CCD or the like in use necessitate such correction.
The optical filter generally includes an infrared cutting filter which is disposed immediately before the solid-state image sensor for the purpose of cutting off an infrared component.
Further, it is necessary to include a low-pass filter for avoiding undesirable phenomena, such as moire fringes caused by the relation between the number of pixels of the solid-state image sensor and the spatial frequency of an object, and a spurious color in the case of a color solid-state image sensor.
Generally, the optical filter of this kind is disposed immediately before the image sensor.
In the case of a solid-state image-sensor camera using a solid-state image sensor of a higher degree of resolution than a solid-state image sensor used for a video camera, a longer period of time is necessary for a process of transferring an image signal recorded on the solid-state image sensor to a storage device. Therefore, a light flux bearing an object image newly falling on the image sensor must be blocked during the process of transferring the image signal. For this purpose, the solid-state image-sensor camera must be provided with a mechanical focal plane shutter which is similar to the focal plane shutter of a camera using silver-halide film.
In the solid-state image-sensor camera based on a silver-halide-film-using single-lens reflex camera, the focal plane shutter is naturally disposed immediately before and near to a focusing image forming plane which corresponds to the position of a silver-halide film. Further, a main reflection mirror (main mirror) arranged to guide an object image light flux to a viewfinder optical system for viewing and confirming the object image by the photographer and an auxiliary reflection mirror (sub-mirror) arranged to guide a part of the object image light flux to an automatic focusing optical system are arranged to be retracted by a mirror driving device away from the path of a photo-taking light flux leading from a photo-taking lens to the solid-state image sensor when an exposure is made. However, since the mirror driving device and other associated parts are disposed immediately before the focal plane shutter, it has been difficult to secure a space for arranging the above-stated optical filter members such as the low-pass filter immediately before the solid-state image sensor.